Dynamic characteristics of a high-speed air-bearing spindle and their effects on surface generation in ultra-precision machining

Abstract

In ultra-precision machining, a high-speed air-bearing spindle (HS-ABS) is a key component with high rotational accuracy, which can machine high-quality surfaces with nanometric surface roughness and sub-micrometric form error. The dynamic characteristics of the HS-ABS play a crucial role in affecting the machined surface quality. However, there is still a research gap on the dynamic characteristics of an HS-ABS under multiple degrees of freedom, especially about the effects on surface generation in ultra-precision diamond milling (UPDM). In this paper, a nonlinear dynamic model was first developed to clarify the dynamic characteristics of the HS-ABS under five degrees of freedom with three translations and two tilting motions. Second, a surface generation model was proposed to study the surface topographies formed under the dynamic characteristics of the HS-ABS. A series of cutting experiments were conducted to examine the cutting forces and surface topographies. The theoretical and experimental results show that the dynamic characteristics of the HS-ABS have: (1) an axial natural frequency with small nonlinear variation, producing regular straight patterns with slight deformation at the machined surface; (2) a radial natural frequency with significant nonlinear variation, forming regular diagonal patterns with remarkable deformation, and minor chaos generating slight random fluctuation; (3) twin tilting natural frequencies with significant nonlinear variation, causing regular diagonal or straight patterns with remarkable deformation and inevitable chaos generating apparent random fluctuation, even deflection. This study provides a comprehensive understanding of the dynamic characteristics of the HS-ABS and the surface formation mechanisms under the HS-ABS's dynamic characteristics in ultra-precision machining.